IO#wait

static VALUE
io_wait(int argc, VALUE *argv, VALUE io)
{
#ifndef HAVE_RB_IO_WAIT
    rb_io_t *fptr;
    struct timeval timerec;
    struct timeval *tv = NULL;
    int event = 0;
    int i;

    GetOpenFile(io, fptr);
    for (i = 0; i < argc; ++i) {
        if (SYMBOL_P(argv[i])) {
            event |= wait_mode_sym(argv[i]);
        }
        else {
            *(tv = &timerec) = rb_time_interval(argv[i]);
        }
    }
    /* rb_time_interval() and might_mode() might convert the argument */
    rb_io_check_closed(fptr);
    if (!event) event = RB_WAITFD_IN;
    if ((event & RB_WAITFD_IN) && rb_io_read_pending(fptr))
        return Qtrue;
    if (wait_for_single_fd(fptr, event, tv))
        return io;
    return Qnil;
#else
    VALUE timeout = Qundef;
    rb_io_event_t events = 0;
    int i, return_io = 0;

    /* The documented signature for this method is actually incorrect.
     * A single timeout is allowed in any position, and multiple symbols can be given.
     * Whether this is intentional or not, I don't know, and as such I consider this to
     * be a legacy/slow path. */
    if (argc != 2 || (RB_SYMBOL_P(argv[0]) || RB_SYMBOL_P(argv[1]))) {
        /* We'd prefer to return the actual mask, but this form would return the io itself: */
        return_io = 1;

        /* Slow/messy path: */
        for (i = 0; i < argc; i += 1) {
            if (RB_SYMBOL_P(argv[i])) {
                events |= wait_mode_sym(argv[i]);
            }
            else if (timeout == Qundef) {
                rb_time_interval(timeout = argv[i]);
            }
            else {
                rb_raise(rb_eArgError, "timeout given more than once");
            }
        }

        if (timeout == Qundef) timeout = Qnil;

        if (events == 0) {
            events = RUBY_IO_READABLE;
        }
    }
    else /* argc == 2 and neither are symbols */ {
        /* This is the fast path: */
        events = io_event_from_value(argv[0]);
        timeout = argv[1];
    }

    if (events & RUBY_IO_READABLE) {
        rb_io_t *fptr = NULL;
        RB_IO_POINTER(io, fptr);

        if (rb_io_read_pending(fptr)) {
            /* This was the original behaviour: */
            if (return_io) return Qtrue;
            /* New behaviour always returns an event mask: */
            else return RB_INT2NUM(RUBY_IO_READABLE);
        }
    }

    return io_wait_event(io, events, timeout, return_io);
#endif
}